A Study on the Impact of Good Teachers Sparks National Attention

February 01, 2012

Teachers who succeed in raising standardized test scores have a lasting influence on their students’ lives, helping them avoid teenage pregnancy, go to college and earn more money as adults, according to new research from Columbia and Harvard economists that has attracted widespread attention from partisans in the education reform debate including President Barack Obama in his recent State of the Union message.

The researchers focused on a relatively new way to judge teacher performance called “value-added” (VA), which rates teachers by their impact on student test scores. Teachers’ VA is defined as the average test-score gain for their students, adjusted for differences across classrooms such as prior test scores. School districts from Washington, D.C. to Los Angeles have started to use VA to evaluate teachers.

The method has come under fire from critics, who say that test scores don’t reflect the totality of a teacher’s performance. They also say VA unfairly penalizes teachers assigned lower-achieving students and only measures the ability to “teach to the test.”

To examine these critiques, the researchers built a vast database of 2.5 million children in grades three through eight in a large urban school district and tracked 1 million of them through adulthood. Their working paper was published in December by the National Bureau of Economic Research, a private, nonpartisan organization focused on economic research. It is based in Cambridge, Mass.

The study, which looked at test scores and later measures of achievement, including tax returns and college attendance, found that VA accurately captures teachers’ impact on students’ academic achievement and also improves students’ prospects as adults.

“We find that students assigned to higher VA teachers are more successful in many dimensions,” writes Jonah Rockoff, the Sidney Taurel Associate Professor of Business at Columbia and his Harvard colleagues Raj Chetty and John N. Friedman. “They are more likely to attend college, earn higher salaries, live in better neighborhoods and save more for retirement. They are also less likely to have children as teenagers.”

The research, which comes amid a fierce national debate over the best way to evaluate teacher performance, has attracted a lot of attention. New York Times columnist Nicholas D. Kristoff called it a “landmark” study while the blog of the Albert Shanker Institute, a think tank supported by the American Federation of Teachers, dubbed it “one of the most dense, important and interesting analyses on this topic in a very long time.”

The research was embraced by opponents of teacher tenure and other job protections for teachers, with numerous commentators citing one particular quote from one of the study authors. “The message is to fire people sooner rather than later,” Friedman told the Times in a front-page article on Jan. 6.

Rockoff said Friedman was referring to research which showed that if a district were to institute a policy of firing low VA teachers, “there are greater benefits to doing so early on, before they have lowered the achievement trajectories of many classrooms full of students.”

Skeptics of the value-added method have weighed in as well, including Diane Ravitch, Research Professor of Education at New York University, who believes that the analysis “points us to an education system in which tests become even more consequential than they are now.”

“There would be even less time in our schools than now for the arts, history, civics, geography, the sciences, foreign languages, health, and physical education,” she wrote in a post this month on SOETalk, a blog of the Johns Hopkins University School of Education. “There would be less time to read challenging literature. There would be less time for science experiments. There would be less time for field trips to museums or historical sites. There would be less time for anything other than getting ready for the state tests.”

In another of its widely cited findings, the analysis showed that replacing a teacher whose VA is in the bottom 5 percent with one of average quality would boost an average classroom’s lifetime earnings by about $266,000. Obama mentioned that aspect of the study in his State of the Union address while talking about the importance of public education: “We know a good teacher can increase the lifetime income of a classroom by over $250,000,” he said.

While the study argues that “great teachers create great value,” it notes the difficulties inherent in using VA to evaluate teachers fairly. For instance, an emphasis on VA could lead teachers to cheat or teach to the test, which would then diminish the reliability of VA as a measure of teacher quality.

The authors conclude by noting that while their calculations “show that good teachers have great value, they do not by themselves have implications for optimal teacher salaries or merit pay policies.”

“The most important lesson of this study,” they write, “is that finding policies to raise the quality of teaching—whether via the use of value-added measures, changes in salary structure or teacher training—is likely to have substantial economic and social benefits in the long run.”